The present invention relates to a low-temperature curing epoxy resin composition, and more particularly to an epoxy resin composition which may be rapidly cured at a low temperature and which may be prepared as a cured body excellent in wear resistance, adhensiveness and resistance to hot water.
Epoxy resin is excellent in heat resistance, wear resistance, water resistance and the like and has been conventionally applied to a variety of uses such as adhesives, a coating agent and the like.
Most of the epoxy resin is of the two-part curing type. Used as a curing agent is aliphatic amine, aromatic amine, acid anhydride or the like containing active hydrogen in the molecules thereof.
However, when such a curing agent is used, the reactivity of the curing agent is considerably low at a low temperature not higher than 5.degree. C. Further, the resultant cured body is poor in mechanical strength. Accordingly, as an epoxy resin curing agent to be used under a low-temperature condition, mercaptan or low-molecular-weight aliphatic amine has been conventionally used.
The use of such a curing agent presents the following problems.
(1) When mercaptan is used as the curing agent, the mercaptan gives out an extremely offensive smell, thus lowering the work efficiency. Further, the resultant cured body is very fragile and is also very poor in resistance to hot water. PA0 (2) When low-molecular-weight aliphatic amine is used as the curing agent, the low-molecular-weight aliphatic amine is volatile so that the resin composition is susceptible to change and is therefore unstable. Further, the low-molecular-weight aliphatic amine is an irritant to the skin, thus lowering the work efficiency. Further, the resultant cured body is fragile because its cross-linking density is too high. PA0 (a) an epoxy resin main agent to which unsaturated acid ester of polyhydric alcohol is added and which contains epoxy resin having urethane bonds in the molecules thereof; and PA0 (b) a curing agent containing an alicyclic amine compound.
As other method of curing the epoxy resin at a low temperature than the method above-mentioned, there has been proposed a method including a step of adding, to epoxy resin, unsaturated acid ester of polyhydric alcohol which may rapidly achieve an addition reaction (Michael reaction) with amine even at a low temperature, so that the reactivity of the epoxy resin at a low temperature is improved with the use of generated reaction heat (Japanese Patent Unexamined Publication No. 8043/1977).
However, the number of functional groups per molecule in unsaturated acid ester of polyhydric alcohol is generally as small as 1 to 3. Accordingly, when unsaturated acid ester of polyhydric alcohol is added to epoxy resin, the resultant cured body presents a small cross-linking density, so that the mechanical strength thereof is insufficient. Further, such a method presents the defect that the cured body is considerably lowered in resistance to hot water due to the addition of unsaturated acid ester of polyhydric alcohol.
Alternately, there has been proposed a method using, as a main agent, a mixture of epoxy resin with unsaturated acid ester of polyfunctional polyhydric alcohol having 3 to 6 functional groups per one molecule, and also using polyamide as a curing agent, thereby to improve the resistance to hot water of the resultant cured body (Japanese Patent Unexamined Publication No. 179524/1987). However, under such severe conditions that the resultant cured body is immersed in hot water of about 70.degree. to 100.degree. C. for several weeks, the cured body presents no sufficient strength and presents tucks on the surface thereof.
Meanwhile, the inventors of the present invention have obtained a low-temperature curing epoxy resin composition by curing, with an alicyclic amine compound, an epoxy resin main agent which contains unsaturated acid ester of polyfunctional polyhydric alcohol having 3 to 6 functional groups at a ratio of 5 to 30 parts by weight for 100 parts of the epoxy resin main agent. This composition may be cured even at a low temperature and may be prepared as a cured body excellent in resistance to hot water. However, such a cured body is slightly fragile and therefore apt to be broken due to a shock or the like.